Preparation and properties of heavily doped and strongly compensated Ge films on GaAs

We present and generalize the preparation conditions and properties of heavily doped and strongly compensated (HDSC) Ge films obtained by deposition in the vacuum onto the semi-insulating GaAs (100) substrates. A possibility of formation of Ge films with various doping levels and compensation degrees (in particular, fully compensated) is demonstrated. Heavily doped and fully compensated Ge single-crystalline thin (∼0.1 μm) films obtained have high resistivity (up to 140 Ω cm), conductance activation energy as high as half the bandgap of Ge, low free charge carrier mobility (∼50 cm2/V s), and concentration (∼1014–1015 cm−3). The electrical and optical properties of the films are explained with allowance made for the presence of large-scale fluctuations of electrostatic potential in Ge. Under certain conditions, a two-dimensional potential relief may exist in thin HDSC Ge films, as well as two-dimensional percolation may occur.